Optical devices, such as laser diodes (LD) and light emitting diodes (LED) can be fabricated by crystal growth of a nitride-based group III-V compound semiconductor on a sapphire substrate, a SiC substrate, etc. As technical problems for optical devices of this type, there are improvements in heat dissipation performance and light extraction efficiency.
Recently, there has been proposed a technique in which a problem of heat dissipation performance can be solved and large current operation is feasible by bonding a nitride-based group III-V compound semiconductor to a substrate superior to a sapphire substrate or a SiC substrate in heat dissipation performance and peeling off the substrate by a laser lift-off method.
It is common to perform thermo compression bonding when a nitride-based group III-V compound semiconductor on a sapphire substrate is bonded to a substrate with excellent heat dissipation performance (see, U.S. Patent Application Publication No. U.S. 2007/0,298,587.)
However, there is a case in which a sapphire substrate or a SiC substrate has already been bended before the bonding. Moreover, voids may be formed in the vicinity of the bonded surfaces or an adhesion force may be reduced due to the heat at the time of thermo compression bonding and the strength of a bonding force. Because of this, a problem such as cracking or peeing-off of a GaN thin film may occur during laser lift-off and cracking of a support substrate.
As a technique to form a support substrate, besides the bonding of the substrate described above, there is a technique to grow a thick metal film by plating in order to use the plated metal film as the substrate, which achieves reduction of the process steps and cost. Nevertheless, when a thick metal film is formed on the compound semiconductor described above by plating, a problem such as diffusion of the plated metal may occur. It is thus not easy to perform a process of combining the laser lift-off and plating.